Conventionally, as an electric connection box, the one disclosed in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2006-19711) is known. The electric connection box is configured by housing a board for mounting a heat generating component in a casing. A metal heat collecting part is fixed to the above described board, and a cylindrical part exposed to an outside of the casing is fixed to the heat collecting part. A heat dissipation window is formed in an upper portion of the cylindrical part, and an intake window is formed in a lower portion.
In the above described electric connection box, heat generated from the heat generating component is transferred to the cylindrical part, which is exposed to the outside of the casing, through the heat collecting part from the board. The heat transferred to the cylindrical part is transferred to air flowing in from the intake window, and the air rises in the cylindrical part to flow out from the heat dissipation window, whereby the heat is dissipated to the outside of the casing.
However, according to the above described configuration, the cylindrical part is provided at the outside of the casing, and therefore, downsizing of the electric connection box cannot be achieved.
Thus, it is conceivable that downsizing of the electric connection box is achieved by omitting the cylindrical part and the heat generating from the heat generating component is dissipated to the outside of the casing by providing an air hole at a top and bottom of the casing. According to the configuration, external air flows toward the air hole at an upper portion from the air hole at a lower portion inside the casing, and therefore, it is expected that the heat generated from the heat generating component can be dissipated to the outside of the casing by the flow of the external air.
However, the shape of the casing is not always cylindrical, and the flow path of air becomes complicated due to electronic components on the circuit board housed in the casing. Therefore, it is feared that air does not flow smoothly in the casing and the heat of the heat generating component is confined within the casing.